A starter of a motor vehicle generally comprises an electric motor, a transmission mechanism, a control mechanism and the like. In the starting procedure of the vehicle engine, the electric motor generates a rotational torque which is transmitted to a gear ring on a flywheel of the engine via a driving gear of the transmission mechanism to drive a crank shaft of the engine to rotate.
The control mechanism controls the ON/OFF state of a main circuit of the starter, and controls the engagement and disengagement between the driving gear and the gear ring. Nowadays, a solenoid switch is generally used as the control mechanism of the starter. FIG. 1 is a schematic view of the structure of a current solenoid switch of the starter. The solenoid switch mainly comprises a solenoid core 4 and windings 6, all fixedly mounted in a housing 2, two contact studs 10 carried by a cap 8 which is fixed to the housing 2, a solenoid armature 16 axially movable in the inner side of the windings 6, a switching shaft 12 carried by the solenoid core 4 and the solenoid armature 16 in a manner of being axially movable relative to them, an actuating bar 18 fixed to the solenoid armature 16, a striking bar 20 fixed in the solenoid armature 16, a contacting bridge 14 mounted to a back end of the switching shaft 12, etc. The actuating bar 18 is movably connected at its front end with a pinion engaging lever (not shown).
A back end of the solenoid core 4 and a front end of the cap 8 are clamped between a step 22 formed in a back portion of the housing 2 and a crimped inward flange 24 formed by the back end of the housing 2, facing towards each other. A disk spring 21 is disposed between the solenoid core 4 and the cap 8, the disk spring 21 being compressed in the axial direction to a full extent, without any ability of further axial deformation.
When a driver starts the vehicle by an ignition key, an electro-magnetic force is generated in the solenoid armature 16 by the windings 6, under which force the solenoid armature 16 moves backwards towards the solenoid core 4. When the striking bar 20 comes into contact with the switching shaft 12, the striking bar 20 pushes the switching shaft 12 to move axially backwards together with it. The contacting bridge 14 is moved together with the switching shaft 12 until it comes into contact with the two contact studs 10 to electrically connects them, thereby a main circuit of the electric motor is switched on to drive the electric motor to rotate. After the contacting bridge 14 comes into contact with the two contact studs 10 and thus establishes electric connection between the two contact studs 10, the solenoid armature 16 continues to move by a distance towards the solenoid core 4, until it strikes the solenoid core 4 and is stopped by it. During this stage, the front end of the actuating bar 18 pushes the transmission mechanism via the pinion engaging lever, so that the driving gear moves forwards to be engaged with the gear ring on the flywheel of the engine, thereby the engine is started.
In the vehicle starting period, when the solenoid armature 16 strikes the solenoid core 4, an axial striking force thus generated is transmitted from the solenoid core 4 to the crimped portion 24 via the disk spring 21 and the cap 8. The crimped portion 24 may be elastically deformed backwardly and radially outwardly since the thickness of it is relatively small. In this condition, the cap 8 will quickly bounce backwards by a very small distance. Then, as the striking force disappears, the cap 8 gradually comes back to its original position in a vibrated manner. In the short period of the backward bouncing of the cap 8, the contact studs 10 carried by it also bounce backwards quickly, but the contacting bridge 14 cannot completely follow the backward bouncing action of the contact studs 10. Thus, the contacting bridge 14 and the contact studs 10 may be out of contact, which will result in instantaneous break of the main circuit of the electric motor. Such an instantaneous break may cause an instantaneous deep drop of the electric current in the main circuit of the electric motor, which may affect the operation of the electric motor. Meanwhile, an electric arc will be created between the contacting bridge 14 and the contact studs 10. It is known from test that the maximum power of this electric arc may be up to 30 kW, and the heat thus generated may be up to 8 Joule. This energy may result in burning and adhesion between the contacting bridge 14 and the contact studs 10.